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.\" $OpenBSD: syscall.2,v 1.8 2005/04/16 18:19:59 otto Exp $
.\" $NetBSD: syscall.2,v 1.4 1995/02/27 12:38:53 cgd Exp $
.\"
.\" Copyright (c) 1980, 1991, 1993
.\" The Regents of the University of California. All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. Neither the name of the University nor the names of its contributors
.\" may be used to endorse or promote products derived from this software
.\" without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" @(#)syscall.2 8.1 (Berkeley) 6/16/93
.\"
.Dd June 16, 1993
.Dt SYSCALL 2
.Os
.Sh NAME
.Nm syscall ,
.Nm __syscall
.Nd indirect system call
.Sh SYNOPSIS
.Fd #include <sys/syscall.h>
.Fd #include <unistd.h>
.Ft int
.Fn syscall "int number" "..."
.Fn __syscall "quad_t number" "..."
.Sh DESCRIPTION
.Fn syscall
performs the system call whose assembly language
interface has the specified
.Fa number
with the specified arguments.
Symbolic constants for system calls can be found in the header file
.Ao Pa sys/syscall.h Ac .
.Pp
Since different system calls have different return types, a
prototype of
.Nm __syscall
specifying the correct return type should be declared locally.
This is especially important for system calls returning
larger-than-int results.
.Pp
The
.Nm __syscall
form should be used when one or more of the parameters is a
64-bit argument to ensure that argument alignment is correct.
This system call is useful for testing new system calls that
do not have entries in the C library.
.Sh RETURN VALUES
The return values are defined by the system call being invoked.
In general, for system calls returning
.Va int ,
a 0 return value indicates success.
A \-1 return value indicates an error,
and an error code is stored in
.Va errno .
.Sh HISTORY
The
.Fn syscall
function call appeared in
.Bx 4.0 .
.Sh BUGS
There is no way to simulate system calls that have multiple return values
such as
.Xr pipe 2 .
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